Space Telescope Science
Albert Einstein reshaped our understanding of the fabric of space. In his general theory of relativity in 1915, he proposed the revolutionary idea that massive objects warp space, due to the effects of gravity. Until that time, Isaac Newton's theory of gravity from two centuries earlier held sway: that space was unchanging. Einstein's theory was experimentally verified four years later when a team led by British astronomer Sir Arthur Eddington measured how much the sun's gravity deflected the image of a background star as its light grazed the sun during a solar eclipse. Astronomers had to wait a century, however, to build telescopes powerful enough to detect this gravitational warping phenomenon caused by a star outside our solar system. The amount of deflection is so small only the sharpness of the Hubble Space Telescope could measure it.
Hubble observed the nearby white dwarf star Stein 2051 B as it passed in front of a background star. During the close alignment, the white dwarf's gravity bent the light from the distant star, making it appear offset by about 2 milliarcseconds from its actual position. This deviation is so small that it is equivalent to observing an ant crawl across the surface of a quarter from 1,500 miles away.